She said in new documentary Becoming Chaz: "I was hysterical one day because I was calling Chaz's answering machine and I realized it was her old voice, and then I said, 'Chaz is there a way I can save it because I will never hear that voice again?' And there wasn't, it was gone.

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"That's the most traumatic thing that has happened to me in this whole thing - hearing her voice and knowing I'll never hear it again."

The 64-year-old admitted that she avoided seeing Bono for a long time after her procedure because she was "terrified".

She explained: "I was so nervous. I hadn't seen her and I was putting it off.

"My boyfriend finally said, 'This is crazy, just do it.' I said, 'I'm so terrified of what will happen. If I don't recognize her, what will happen?'"

Cher also admitted that she finds it difficult to remember to refer to her offspring as "him" rather than "her".

She added: "At some point, I'm gonna have to start calling her 'him'. It doesn't seem comfortable to me yet. Actually I just can't remember and I guess I'll start forcing myself but I'm not sure she cares."